1. Field of the Invention
The present invention relates to an ignition timing control device of an internal combustion engine and particularly to a technique of controlling ignition timing based on a waveform of vibration generated in the internal combustion engine.
2. Description of the Background Art
Conventionally, there have been proposed various methods of determining whether knocking (knock) is present or absent. A knock control device of an internal combustion engine described in Japanese Laid-Open Patent Publication No. 2003-021032 includes a knock sensor for detecting a knock of the internal combustion engine, a statistical processing portion for statistically processing an output signal detected by the knock sensor, a first temporary determination portion for determining whether or not the knock has occurred based on a processing result by the statistical processing portion, a second temporary determination portion for determining whether or not the knock has occurred based on a waveform of the output signal detected by the knock sensor, and a final knock determination portion for finally determining whether or not the knock has occurred based on the results of the knock temporary determination by the first temporary determination portion and the knock temporary determination by the second temporary determination portion. The final knock determination portion finally determines that whether or not the knock has occurred when both the first temporary determination portion and the second temporary determination portion determine that the knock has occurred.
With the knock control device described in this official gazette, the knock temporary determination by a statistical processing program and the knock temporary determination by a waveform program are used and it is finally determined that the knock has occurred only when it is determined that the knock has occurred in the respective temporary determinations. Thus, with regard also to an output signal based on which knocking was detected erroneously by knocking determination using only one of the statistical processing program and the waveform program, it is possible to accurately determine whether or not the knocking has occurred.
However, in the knock control device described in Japanese Laid-Open Patent Publication No. 2003-021032, the knocking determination by the statistical processing and the knocking determination by a shape of the waveform are performed independently of each other. Therefore, accuracy of each determination method is not improved and deterioration of the accuracy by a noise component is not resolved in each determination method. Therefore, the device is susceptible to further improvement so as to accurately determine whether the knocking is present or absent and to accurately perform retard control of the ignition timing at the time of knocking. Moreover, because the ignition timing is retarded without consideration of a load of the internal combustion engine when the knocking has occurred, the ignition may be conducted at such improper timing that an output of the internal combustion becomes insufficient depending on the load.